Various types of information equipment ranging from a large-capacity server to a mobile terminal have been drastically developed. Along with this development, there have been pursuits for even higher performances in memories or logic devices that constitute information equipment, and non-volatile semiconductor memories or the like are being developed.
In particular, among those non-volatile semiconductor memories, an MRAM (Magnetic Random Access Memory) is capable of high-speed and almost infinite (1015 times or more) rewriting, because data storage is performed by way of the direction of magnetization of a magnetic body. It is expected that the MRAM will be developed in the future for code storage or working memories because of high speed operation and reliability thereof.
Meanwhile, the MRAM has had a difficulty in lowering power consumption or increasing capacity because magnetization is reversed by a current magnetic field generated from wiring.
As one method to solve the problem, there has been studied recording without the use of a current magnetic field, that is, a magnetization reversal system. In particular, researches on spin torque magnetization reversal are active (see, for example, Non-Patent Literatures 1 and 2).
A storage device using the spin torque magnetization reversal is typically constituted of an MTJ (Magnetic Tunnel Junction) (TMR (Tunneling Magnetoresistive)) device.
The configuration thereof uses the fact that a spin polarized electron that passes through a magnetic layer fixed in a certain direction gives, when entering another free magnetic layer (with a direction unfixed), torque to the magnetic layer (this is also called spin injection torque). Feeding a current of a certain threshold value or more allows the free magnetic layer to be reversed. Rewriting of 0/1 is performed by changing a polarity of a current. Hereinafter, an MRAM using the spin torque magnetization reversal will be referred to as an ST-MRAM (Spin Torque-Magnetic Random Access Memory). The spin torque magnetization reversal is also referred to as spin injection magnetization reversal. There is a great expectation about the ST-MRAM as a non-volatile memory that enables low power consumption and large capacity while maintaining advantages of the MRAM, that is, high-speed and almost infinite times of rewriting.
By the way, in the ST-MRAM, time for spin torque magnetization reversal largely depends on an initial angle of magnetization at the time when the application of a current starts. In other words, the initial angle of magnetization varies because of thermal fluctuation or the like, and thus the time for magnetization reversal varies. As a result, in order to reliably perform magnetization reversal, it is necessary to elongate a write pulse or increase a voltage, and there may be concern about lowering in write speed, increase in power consumption, or the like.
In this regard, there is conceived a method of providing a two-layer configuration including a layer of an in-plane magnetization film and a layer of a perpendicular magnetization film, coupling those layers to each other by magnetic interaction with an appropriate magnitude to impart an appropriate initial angle to the layer of the in-plane magnetization film, and suppressing variations in reversal time of spin torque reversal (see Patent Literatures 1 and 2).